This invention relates to an absorption refrigeration system and, in particular, to an improved apparatus for purging an absorption refrigeration system of non-condensable gases.
Non-condensable gases such as air, hydrogen, nitrogen and the like can find their way into absorption refrigeration systems during normal processing of the working substances or through leaks in the various system components. These non-condensables, if allowed to build up in the system, act to increase the pressure within the machine thereby reducing the machine's capacity. The non-condensables accumulate in the low pressure region of the system which is the absorber. It is the general practice to draw the non-condensables from the absorber and collect them in a purge storage tank which is periodically evacuated to ambient. The recommended means for evacuating the tank are to attach a vacuum pump to the tank and pump the non-condensables from the low pressure tank directly to the surrounding ambient.
One major problem with the use of a vacuum pump in association with a low pressure purge storage tank is the danger of oil from the pump backing up into the tank and then into the system. Even a slight amount of oil entering the system can have a harmful effect on the machine operation and performance. One prevalent way in which oil from the vacuum pump can quickly find its way into the system through the purge tank is during a power failure, occurring when the purge valve is open. Typically, at this time the purge tank is at a pressure of about 1/100 atmospheres and the pump discharge is at atmospheric pressure. This large pressure difference serves to push the oil in the pump rapidly back into the tank and then further into the absorption system.
Normally, the non-condensables along with water vapor and absorbent which, for purposes of this disclosure, is lithium bromide are present in the purge tank. Activating the purge vacuum pump brings the water vapor and a small quantity of LiBr in contact with the pump oil. When the pump is shut down, air is permitted to enter the pump through the pump discharge. The mixture of lithium bromide, water vapor and air has been found to be highly corrosive and can lead to early pump failure.